This invention relates to novel photosensitive materials having improved developing performance and shelf stability, and more particularly, to novel heat-developable photosensitive materials having improved developing performance and shelf stability.
Photographic processes using silver halides have been most widely used because of their superior photographic characteristics such as sensitivity and gradation control as compared with other photographic processes including electrophotography and diazo processes. A recent innovation in the process for treating a silver halide-based photosensitive material for image formation is the development of a new dry treatment technique capable of readily and quickly producing images by heating as a substitute for the conventional wet technique using developing solution.
Heat developable photosensitive materials and their image forming processes are well known in the art and described in the literature, inter alia, "Fundamentals of Photographic Engineering--Non-Silver Salt Photography--", Corona Publishing K.K., Tokyo, Japan (1982), pages 242-255; "Image Information", April 1978, page 40; and Nebletts Handbook of Photography and Reprography, 7th ed. Van Nostrand Reinhold Company, pages 32-33; U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020, and 3,457,075; British Pat. Nos. 1,131,108 and 1,167,777; and Research Disclosure, June 1978, pages 9-15 (RD 17029).
A number of methods have been proposed for producing color images through heat development. For example, a process for forming color images through reaction of an oxidant of a developing agent with a coupler is known, U.S. Pat. No. 3,531,286 disclosing p-phenylene diamine reducing agents and phenolic or active methylene couplers; U.S. Pat. No. 3,761,270 disclosing p-aminophenol reducing agents; Belgian Pat. No. 802,519 and Research Disclosure, September 1975, pages 31-32, disclosing sulfonamide phenol reducing agents; and U.S. Pat. No. 4,021,240 disclosing a combination of a sulfonamide phenol reducing agent and a four equivalent coupler.
These processes, however, have the drawback that color images become turbid as images of reduced silver and color images are concurrently created in exposed areas after heat development. Typical solutions to this problem are by removing silver images by liquid treatment and by transferring only the dye to another layer, for example, an image-receiving layer on another sheet. It is, however, very difficult to distinguish unreacted reagents and the dye to enable the transfer of the dye only. Furthermore, the above-mentioned processes generally take a relatively long time in development and produce images having relatively high fog and low density.
A new type of image forming process using silver halide was developed to overcome these drawbacks, the process comprising imagewise forming a mobile dye and transferring the dye to a dye-fixing layer (see Japanese Patent Application Kokai Nos. 58-149046, 59-154445, 59-165054, and 59-180548, U.S. Pat. Nos. 4,503,137, 4,474,867, 4,483,914, and 4,455,363). These processes use a photosensitive material comprising a silver halide and a dye-providing substance which acts on the silver halide as a reducing agent at elevated temperatures and is itself oxidized to release a mobile dye. The material is heated in the substantial absence of water during or after exposure to light, thereby forming a mobile dye imagewise.
The image forming process of this type requires at least two steps, a step of forming a mobile dye imagewise by heating and a step of transferring the dye to a dye-fixing layer. As it is desirable to make the treatment more quick and simple, an image forming process capable of carrying out these two steps at the same time is proposed (see Japanese Patent Application Kokai No. 59-218443).
In general, these image forming processes use a reducing agent other than the common reducing agents (assigned to react with the silver halide as mentioned above) for the purposes of accelerating reaction of silver halide with a common reducing agent, preventing an oxidant of a common reducing agent from migrating to any layer other than the destined to give rise to color mixing, suppressing air oxidation of any compounds in the photosensitive material, and preventing fogging. Exemplary compounds effective as such secondary reducing agents are hydroquinone, alkyl-substituted hydroquinones such as t-butylhydroquinone and 2,5-dimethylhydroquinone, catechols, pyrogallols, halogen-substituted hydroquinones such as chlorohydroquinone and dichlorohydroquinone, alkoxy-substituted hydroquinones such as methoxyhydroquinone, and polyhydroxybenzene derivatives such as methylhydroxynaphthalene. Also effective are methyl oleate, ascorbic acid, ascorbic acid derivatives, hydroxylamines such as N,N'-di-(2-ethoxyethyl)hydroxylamine, pyrazolidones such as 1-phenyl-3-pyrazolidone, 4-methyl-4-hydroxymethyl-1-phenyl-3-pyrazolidone, reductones, and hydroxytetronic acids.
If these reducing agents are directly added to photosensitive materials, they tend to deteriorate the shelf stability of photosensitive material, lower their development accelerating effect with a lapse of time, and cause fogging. Thus the reducing agent is usually kept isolated from an emulsion layer until the time of development treatment, for example, by adding the agent to a developing solution.
It would advantageously provide a more quick and simple development treatment if a reducing agent having aging resistance can be directly incorporated in the photosensitive material, specifically in an emulsion layer or the like.